4. COMPARISON WITH PREVIOUS WORK

The goal of this paper is to determine the absolute age of the universe
t0(h, m,
).
Knowledge of h alone cannot be used to determine t0
with much accuracy.
For example, the estimate h = 0.68 ± 0.10 corresponds to 8 <
t0 < 22 Ga
(Fig. 4).
Similary, knowledge of (m,
) yields
H0t0
(m,
) not
t0(H0 is the usual Hubble constant).
When one inserts a preferred value of h into a
H0t0 result, one
is not taking into consideration
the correlations between preferred h values and preferred
(m,) values
that are inherent, for example, in
CMB(h,
m,)
and baryons(h,
m).
The preferred values of h in these likelihoods depend on
m and
.
Perlmutter et al.
(4)
used SNe measurements to constrain
(m,
) and
obtained values for H0t0. To obtain
t0, they did the analysis with h
set equal to the value preferred by their SNe data, h = 0.63.
Their result is t0 = 14.5 ± 1.0 (0.63 / h) Ga.
When a flat universe is assumed, they obtain
t0flat =
14.9+1.4-1.1 (0.63 / h) Ga.
Riess et al. (5)
found h = 0.65 ± 0.02 from their SNe data.
Marginalizing over this Hubble value and over
and
m,
they report t0 = 14.2 ± 1.7 Ga.
When a flat universe is assumed, their results yield
t0flat = 15.2
± 1.7 Ga. The Perlmutter et al.
(4) and Riess
(5)
results are in good agreement.
When I assume h = 0.64 ± 0.02, I get
t0 = 14.6+1.6-1.1 Ga.
This result is plotted in
Fig. 2 to illustrate the important
influence on the result of using a small h uncertainty.
Efstathiou et al.
(12),
on the basis of a combination of CMB and
Perlmutter et al.
(4)
SNe data, have
estimated t0 = 14.6 (h / 0.65)-1 Ga.
I used h = 0.65 ± 0.0 with this data combination to get
t0 = 14.5+1.2-1.0 Ga. However,
when I used h = 0.65 ± 0.10,
the result is 0.7 Gy lower (t0 =
13.8+3.2-1.4 Ga).
To obtain the main result, I used uncertainties large enough to reflect
our knowledge of h
on the basis of many sources. The use of a larger h uncertainty
contributes to the substantially younger ages found here
(23).

A potential problem with the SNe ages is the high region,
(m,)
(0.8, 1.5), which
dominates the SNe fit.
This region is strongly disfavored by the six other constraints
considered here (see Fig. 3).
These high (m,
) values allow lower ages than the
t0flat SNe
results because the slope of the iso-t0 contours
(Fig. 3B) is larger than the slope of the
SNe contours.
The t0flat results are not as subject to
this problem and are the results most analogous to the
result reported here, despite the fact that the SNe
t0flat results are
less consistent with the result reported here.
There are several independent cosmological measurements which have not been
included in this analysis either because
a consensus has not yet been reached
[gravitational lensing limits
(27,
28,
29,
30)]
or because the analysis of the measurements has not been done in a way
that is sufficiently free of conditioning on certain parameters [local
velocity field limits
(31)].
Doubts about some of the observations used here are
discussed in
(32).
There has been speculation recently that the evidence for
is really evidence
for some form of stranger dark energy that we have incorrectly been
interpreting as .
Several workers have tested this idea.
The evidence so far indicates that the cosmological constant interpretation
fits the data as well as or better than an explanation based on
more mysterious dark energy
(4,
33,
34).